In fact, I don't know a fly tying problem that spitting on won't solve
Fritz crowding the eye?.... goz on it, stroke it back.
Marabou flying around all over the palce?... goz on it.
'Doubling' shoulder hackles (folding them in half) ......goz on fingers, stroke into place.
Tying in tips/ends (Peacock herl, fine wire, hackle tips etc etc).... goz on it - sticks like a magnet to wherever you intend to tie it in.
Trouble dubbing? Goz on yer fingers, or rather, lick them then rub together until tacky....
Cock hackle tails all over the place? ......................I think you've got the idea by now